Hey guys i’m new new to sport bikes and recently picked up a cbr600f3. I rode its for 3 days and it ran well the first 2 days and then on the third I have been out riding for around an hour when the bike started backfiring, smelling like gas, and was dying at stop lights. I pulled in to a parking lot then it died again and was very hard to start but i got it going and started to ride home. On the way back it was giving then cutting power every half second or so. I got it home and when i tried to start it again it just cranked and showed no sign of starting.

I would like to note the person who I bought the bike from claimed to have had no problems with it. It had sat for only a couple months when I bought it.

I have started to take off the carbs and noticed some small bits of fuel in the airbox, oil smells like fuel, and fuel on some of the hoses coming off the top of the carbs.

Do I need to do anything other than just draining the oil since it was contaminated with fuel? Im assuming I just need to clean the carbs because a float is stuck? Would this have caused the plugs to foul? Is there anything else I should check?

Thanks guys

 

Hey there and welcome.

Unless you personally know the previous owner, I wouldn't take stock in anything they say. That sounds harsh, but in my experience, it's a safe thing to just start with a blank canvas mentally and begin troubleshooting the issue.

After a bike has sat up, it can run fine for a bit then go south quickly. This is because all the rubber pieces can start to fail when exercised after drying out and being stiff. It's very common.

I would begin looking at your float needle valves to ensure they are functioning as designed.

If you are fuel rich, it can absolutely foul the plugs.

 

Have you checked the compression? It's not related though a good metric to see where the engine is. I never checked and when I finally did it was helpful to know how low it was and to make a decision where to proceed.

 

Even if you put new valves in, they often don't close. I always take and turn the carburetors a few times, you can also shoot a few times with compressed air gently into the supply nozzle.

 

If fuel is getting in the oil and airbox, sounds like you may have a float or two stuck open. Takes a fair amount of fuel to do that to oil. Give the carbs a good cleaning and look at the float needles, needle seats, and floats. Look to see if the floats are not full of fuel and make sure they float. Inspect the float needles. If they’re hard, replace. If they have a ring around them, replace. If the tip is missing, replace. While the carbs are apart, I’d replace the o-rings as who knows if that has ever been done.